What have been denominated "magnesium bicarbonate processes" have been suggested* for the separation of lime and magnesia from mixtures, e.g., dolomite. For example, what has been called the "Pattinson process" involves calcining dolomite, slaking the calcine to form a milk of dolomite, classifying the milk of dolomite to remove impurities, and treating the classified milk of dolomite with washed and compressed kiln gases to precipitate calcium carbonate and form soluble magnesium bicarbonate. The calcium carbonate is then recovered by filtration. The filtrate is boiled for a short time to precipitate basic magnesium carbonate, which, in turn, is recovered by filtration. So far as is known, however, neither the Pattinson process nor any variation thereof which has previously been suggested has been capable of producing a high purity calcium carbonate or magnesium carbonate. FNT *See, for example, a Bureau of Mines publication entitled "Economic Considerations in the Recovery of Magnesia From Dolomite", August, 1943.
The Bureau of Mines publication also teaches that finely divided dolomite could be carbonated to separate the anhydrous magnesium carbonate from the calcium carbonate. However, in practice it is so much easier to bring the magnesia of calcined dolomite into solution as the bicarbonate, than to dissolve the anhydrous magnesium carbonate in raw dolomite, that the cost of calcination is justified.
It has also been suggested* that the calcium carbonate sludge recovered any filtration in the Pattinson process includes magnesian values which can be recovered by re-slurrying the sludge, carbonating, and then recycling the liquor at the slaking step. By this recycling, the plant capacity for production of magnesium products may be increased but the purity of the magnesium carbonate remains the same as in the Pattinson process. FNT *U.S. Pat. No. 2,373,528.